The invention concerns a hydrostatic mechanical wheel drive.
Hydrostatic mechanical wheel drives are used in movable construction machinery and in vehicles for special functions such as dumping, heavy transport, fire fighting, etc. both for wheel and full-track vehicles. They actuate individual wheels or sprocket wheels for driving a caterpillar. The wheels are screwed on a flange of a wheel hub.
The radial space available for the individual wheel drive as a rule is limited by the inner wheel diameter or a pitch circle diameter for fixing bolts. The wheel diameters and pitch circle diameters cannot be enlarged at will, since otherwise the wheels would no longer fit in the vehicle and the expense for added parts would increase, for example, for the tracks, supports, etc., and in the steered wheels the angle of lock would be substantially limited. Within this radial limitation has to be housed, the wheel drive with its mechanical transmission gearing in the form of a planetary gear, with a wheel bearing, a hydraulic lifting piston motor, a cover for a hydraulic connection and with a brake of short axial length and low weight.
DE-A1 27 44 977 shows a wheel drive with an axial piston motor of the swash plate type which has a constant displacement capacity. A highly reducing toothed wheel gearing in the form of a two-step planetary gear makes possible small radial dimensions and a heavy load capacity by the use of tapered roller bearings. The latter are situated between the wheel hub and a wheel hub support in which the hydromotor is accommodated and are rigidly connected with the planet carrier. The length of course is considerable.
To increase the speed range of the vehicle for driving on the road, the wheel drives have a clutch by which individual wheel drives can be disconnected when driving on the road. The reduced total displacement capacity of the remaining wheel drives produces, with the delivery rate of the pump remaining the same, an increased driving speed, but with reduced torque. In addition, the clutch increases the weight considerably, the construction expense and the length of the wheel drive.
As a drive unit can be provided any kind of hydromotor including, for example, a radial-piston motor. Although their construction is axially short, these require more radial space. In addition, in the wheel drive known the drive shaft can extend through on the vehicle inner side in order to mount a brake thereon, and this would further increase the weight and length.
Also known is a wheel drive for a full-track vehicle (Prospectus F 43421/RT 3391-383f of Zahnradfabrik Passau GmbH of the year 1991) in which an axial-piston motor according of the swash plate type is situated in a housing designed as wheel hub support. The swash plate is tiltably supported in a swivel frame and its inclination to the axis of rotation of the axial-piston motor can be adjusted by a lever mechanism and a hydraulic piston whereby changes the displacement capacity and thus the speed of rotation of the axial-piston motor can be achieved. The swash plate can be infinitely varied, there sufficing for many applications two adjusting steps, namely, for a maximum and minimum displacement capacity. This is even advantageous when it is necessary during operation quickly to change between two speed ranges.
Between the housing and the swivel frame, axially offset relative to the axial-piston motor, is a parking brake of multiple disc design with automatic actuation to be closed by a plate spring and hydraulically opened. The brake is thus between the axial-piston motor and a toothed wheel gearing. Thereby, accessibility and cooling are impaired. In addition, the space available is so narrow that the brake cannot with sufficient reliability hold heavy vehicles on slopes.
The invention is based on the problem of providing a compact hydrostatic mechanical wheel drive with a quickly responsive control for a radial-piston motor and a brake which is also suitable for heavy vehicles.